The damaging effects of sunlight on human skin have been recognized since time immemorial and many remedies have been proposed to protect the skin from this damage. In general, harmful ultraviolet (UV) rays, particularly those originating from sunlight, which penetrate the upper atmosphere and reach the earth's surface, can be classified into the following (i) and (ii).
(i) The energy-rich UV-B rays (290 to 320 nm wavelength) which possess an intense physiopathological activity on the skin. These are absorbed just above the dermis and they are responsible for erythema and skin pigmentation.
(ii) UV-A rays (320 to 400 nm wavelength) which penetrate deeper into the skin (to the dermis and beyond). Their energy is much lower than that of UV-B rays and the photobiological effects exhibited by the energy are sustained over a prolonged period of time, for example, they accelerate skin ageing.
Certain organic substances (sunscreen agents) whose molecules absorb the harmful ultra-violet rays have been proposed for use in mitigating the deleterious effects of ultraviolet radiation. Some of these substances absorb more effectively in UV-A range thereby providing a filtering effect of UV radiation in this range, while others are more effective in the UV-B range. However, a common problem exists, whatever the choice of organic sunscreen agent, for protection from any wavelength of ultra-violet radiation. This is that physiological damage to the body can occur, following topical application of these sunscreen agents in amounts necessary to provide effective filtering of harmful ultra-violet radiation. Even those organic sunscreen agents that are believed to be safe for use in this way, necessarily have safety limits imposed, based on the amount applied to the skin. As a result, sufficient protection cannot be obtained for harmful ultra-violet radiation.
Certain inorganic substances have also been proposed for use as sunscreen agents which physically prevent the skin from being exposed to ultraviolet rays. Notable among these is titanium dioxide having a very small particle size. This kind of titanium dioxide is referred to as ultrafine TiO2, affords a good degree of sun blocking potential without exhibiting the unacceptable skin whitening effect observed with the normal pigmentary grade (particle size>300 nm). For example, Patent literature 1 proposes the use of titanium dioxide with an average primary particle size of <100 nm in a water-in-oil emulsion as a sunscreen preparation. Patent literature 1 suggests that organic sunscreen agents such as p-aminobenzoic acid and esters thereof, methoxycinnamate, benzophenone, dibenzoylmethane, and salicylate can also be contained to improve protection. In spite of this, and other prior proposals, there still exists a need for a sunscreen cosmetic composition which has a wide range of protection (i.e. protection for both UV-A and UV-B) in the UV region and is highly efficient and thoroughly safe.
One of the triazine-based ultraviolet absorbers to be used in the present invention is disclosed as an ultraviolet absorber for TAC films in Patent literature 2 below. The other is reported as ultraviolet absorber with large absorption in the short wavelength in Patent literature 3 below. Patent literatures 2 and 3 disclose that these triazine-based ultraviolet absorbers have ultraviolet absorption capability suitable for optical material application and are excellent in performance such as heat deterioration of synthetic resin physical properties. However, there has been no description regarding suggestion of the use of the ultraviolet absorbers for protecting the skin and hair of humans and animals from ultraviolet rays and there has been no disclosure regarding the use of the sunscreen cosmetic composition.
Patent literature 4 below discloses a sunscreen cosmetic containing a di or tri(hydroxyaryl)triazine-based compound. Further, Patent literature 5 below discloses a cosmetic dispensing containing a di(hydroxyaryl)triazine-based compound. However, an ultraviolet protective effect has not been obtained sufficiently and widely by these methods.